1. Field of the Invention
The present invention relates to a portable power supply apparatus, and more particularly, to a portable power supply apparatus for generating microwave plasma, capable of minimizing a power reflected from a plasma generation apparatus and improving power consumption of the plasma generation apparatus by generating the plasma by using a microwave having a specific frequency, monitoring the power reflected from the plasma generation apparatus after the generation of the plasma, detecting a changed impedance matching condition, and correcting the frequency.
2. Description of the Related Art
Recently, plasma treatments have been developed for various applications in the biomedical field such as blood coagulation, sterilization, pasteurization, teeth whitening, and cancer care. In order to use the plasma for the applications in the biomedical field, it is necessary to develop a plasma generation apparatus which can operate to generate the plasma at the atmospheric pressure rather than a plasma generation apparatus used in semiconductor processes where the plasma is generated at a low pressure in a vacuum chamber.
In general, a power required for generating the plasma at the atmospheric pressure is higher than that required at the low pressure in the vacuum chamber.
FIG. 1 is a graph illustrating a relationship between a pressure and an ignition power at the time of generating plasma.
Referring to FIG. 1, it can be seen that an ignition power of about 0.25 W is required to generate the plasma in a low pressure condition, for example, a pressure of about 1 Torr which can be implemented in a vacuum chamber. On the contrary, it can be seen that an ignition power of about 2.5 W is required to generate the plasma in a high pressure condition, for example, the atmospheric pressure of about 760 Torr.
The graph of FIG. 1 illustrates a result of measurement of the power required for generation of the plasma in the plasma generation apparatus according to the pressure condition including the atmospheric. Particularly, the measurement is performed without any gas flow into the plasma generation apparatus. In a case where a gas is flown into the plasma generation apparatus in order to generate a plasma jet, the power for generation of the plasma is further increased.
Therefore, in the conventional atmospheric plasma generation apparatus, a high power is needed to generate the plasma at the atmospheric pressure condition. Accordingly, there is a problem in that a volume and size of the power supply apparatus is too large to carry.
FIG. 2 is a graph illustrating reflection coefficients before and after generation of plasma in a microwave plasma generation apparatus. Hereinafter, the microwave plasma generation apparatus denotes an apparatus for generating plasma by using a microwave as a power source.
In FIG. 2, the graph (a) illustrates a power reflected from the microwave plasma generation apparatus before generation of the plasma, that is, before ignition unloaded, and the graph (b) illustrates a power reflected from the microwave plasma generation apparatus after generation of the plasma, that is, after ignition, where the plasma is generated by using argon (Ar) or helium (He) gas at the atmospheric pressure of 760 Torr with a power of 1 W. Referring to the graph (a) before the generation of the plasma, it can be understood that the microwave plasma generation apparatus is designed to be optimized at a frequency of 875 MHz corresponding to the lowest reflection coefficient.
However, it can also be understood from the graph (b) illustrating the reflection coefficient after the generation of the plasma that the reflection coefficient is changed after the generation of the plasma at the atmospheric pressure by using the microwave plasma generation apparatus which is optimized at the frequency of 875 MHz.
In general, as shown in the graph (b), due to the change in capacitance at the atmospheric pressure, the operating frequency becomes slightly lower than the initial frequency of 875 MHz.
Charged particles such as ions and electrons existing in the generated plasma influence an electric field, so that the capacitance of the plasma generation apparatus becomes different from the initially-designed value. For this reason, the initially-designed impedance matching is changed after the generation of the plasma in the microwave plasma generation apparatus.
Therefore, if the initially-designed frequency of the microwave is supplied to the microwave plasma generation apparatus without any correction, the increase in the reflection power caused from the decrease in the operating frequency cannot be controlled. Accordingly, there is a problem in that an efficiency of power is lowered due to unnecessary power consumption.